Various types of electromagnetic clutches are well known in the prior art and each type of electromagnetic clutch is selected in accordance with the type of driven device.
One of the electromagnetic clutches suitable for use with the compressor of an automobile air conditioner is disclosed in U.S. Pat. No. 4,445,606. That patent discloses an electromagnetic clutch comprising a rotor rotatably mounted on the stationary housing of a driven device through a bearing, a hub fixed on the axial end surface of the drive shaft and an armature disposed such that it is facing one end surface of the rotor with an axial gap therebetween.
A bumper plate is disposed on the outer peripheral portion of the hub to couple it with the hub by means of a toothed structure. An elastic spider is placed between the hub and bumper plate to allow limited rotation of the hub. The bumper plate also faces the armature plate with a gap therebetween, and engages the armature plate through a plurality of leaf springs. Therefore, torsional shock and vibration which is caused by initial attachment of the armature plate to the pole face of the rotor and which acts against the drive shaft is absorbed.
In this type of electromagnetic clutch, the elastic spider is made of an elastic material, for example, a rubber, and attached on the toothed structure of the hub and bumper plate by a vulcanizing process. However, the coupling structure between the bumper plate and the hub is very complicated. As a result, the assembly of the clutch, particularly, the vulcanizing process is a complicated operation. Thus, the cost of the clutch is increased.